Copolyester carbonates are known thermoplastic materials which, due to their many advantageous properties, find use as thermoplastic engineering materials. The copolyester carbonates exhibit, for example, excellent properties of toughness, flexibility and high heat distortion tempertures.
In comparison to aromatic polycarbonates, aromatic copolyester carbonates provide increased Distortion Temperature Under Load, however there is a decrease in the value of certain other properties. Perhaps one of the major differences is in the impact properties for aromatic copolyester carbonate. Impact strength in thin section, 1/8 inch, is significantly reduced in comparison to aromatic polycarbonate. Additionally, a brittle failure mode accompanies the break.
It has now been discovered that various impact modifiers useful in positively modifying the impact properties of aromatic polycarbonate are also useful in upgrading the impact properties of certain aromatic copolyester carbonates while leaving essentially unimproved the impact properties of closely structurally related aromatic copolyester carbonates.